An Internet protocol (Internet protocol, IP for short) multimedia subsystem (IP multimedia subsystem, IMS for short) is a network architecture for implementing extensive network convergence. With development of communications technologies, the IMS can not only implement an initial internet telephony (voice over Internet protocol, VOIP for short) service, but also manage network resources, user resources, and application resources more efficiently, so that a user can move across various networks and use various terminals. Therefore, the IMS is applied more and more widely.
Establishment of the IMS is generally based on a public network. Such networks typically cannot provide carrier-class reliability services, and therefore network faults or device faults frequently occur, causing a failure of an IP phone to contact a central call manager and leading to a working failure of the IP phone and communications interruption of a user. To provide ability to continue local voice communications when a network is faulty, a first existing technology provides a solution: If a domain name system (domain name system, DNS for short) server exists on an IMS network and a DNS proxy (DNS proxy) is deployed on a local gateway, a domain may be configured on an IP phone, and through the DNS server, the IP phone acquires a Session Initiation Protocol (session initiation protocol, SIP for short) server of the domain and a priority of a service of the SIP server in the domain. When the DNS server returns the SIP service to the IP phone, the local gateway inserts, through the deployed DNS proxy, the SIP service of the local gateway into the service priority returned by the DNS server, and advertises them together to the IP phone. A second existing technology provides another solution: When no DNS server exists on an IMS network, multiple SIP servers may be configured on an IP phone and include a SIP service of a local gateway, with sequences of the SIP services serving as priorities. Using the foregoing two technologies, the IP phone may first select an active SIP server and then select a standby SIP server according to service priorities returned by DNS servers or according to a locally configured sequence of the SIP servers; and when all SIP servers are unavailable, the SIP service of the local gateway is selected to provide a basic local call service for the IP phone, thereby implementing failure recovery and local voice survivability.
In a process of implementing the local voice survivability, the inventor finds that at least the following problems exist in the prior art: In the solution according to the first existing technology, in order to implement local survivability, a DNS proxy needs to be configured on the local gateway, so that the SIP service of the local gateway can be inserted into the service priority returned by the DNS server, and if no DNS proxy is configured, the local survivability cannot be implemented; and in the solution according to the second existing technology, different terminals have different local gateways, which need to be configured separately and increase a deployment cost.